超声辅助激光熔注复合涂层晶粒生长研究

发布时间：2018-01-05 22:05

本文关键词：超声辅助激光熔注复合涂层晶粒生长研究　出处：《华东交通大学》2015年硕士论文　论文类型：学位论文

【摘要】：超声辅助激光熔注技术是制备高性能复合涂层的理想方法之一，在航空航天、交通运输等领域具有广泛的应用前景。涂层微观结构对其服役性能起决定作用，因此研究超声辅助激光熔注复合涂层微观结构具有重要意义。本文采用元胞自动机法研究了激光熔注复合涂层的晶粒生长，分析了增强颗粒、非均匀温度场以及超声振动对复合涂层晶粒生长的影响。基于晶界能和曲率驱动机制的晶粒生长理论，建立了单相材料及两相材料晶粒生长元胞自动机模型，分析了增强相SiC颗粒对316L不锈钢复合涂层和AZ91D基板晶粒生长的影响，研究了超声辅助激光熔注复合涂层微观结构的演变机制，并对其进行了实验验证。得出以下结论：（1）316L晶粒生长指数为0.34，，随SiC含量增大和尺寸减小，涂层晶粒尺寸减小；随着熔池深度变化，熔池温度呈指数函数变化，晶粒尺寸逐渐增大。在非均匀温度场下，随SiC颗粒含量增加，其对晶界的钉扎效果逐渐增强；随着SiC颗粒尺寸减小，钉扎效果增强，但是，当SiC颗粒尺寸小于10μm时，晶粒细化机制由晶界钉扎转变为异质形核。（2）随着SiC颗粒加入，镁合金基板的晶粒生长速率变缓，晶粒尺寸变小且均匀；随着SiC尺寸减小，其对基板组织的钉扎效果增强，基板晶粒越细小，组织越均匀，Mg17Al12相越易固溶于α-Mg基体中。（3）随着超声振幅的增大，涂层熔体形核率增大，晶粒尺寸变小，组织越均匀。当振幅为10μm时，超声振动作用下熔体的过冷度为32.23K，形核率为未施加超声振动时的279倍，晶粒细化明显。在超声辅助激光熔注SiC-316L实验中，涂层中SiC颗粒含量越大，涂层晶粒越细小，组织越均匀；SiC颗粒尺寸越小，其对涂层组织的钉扎效果越好，施加超声后的316L涂层组织柱状枝晶更少，晶粒更细小，模拟结果与实验结果吻合。
[Abstract]:Ultrasonic assisted laser melting technology is one of the ideal methods for preparing high performance composite coatings. It has a wide application prospect in aerospace, transportation and other fields. The microstructure of the coating plays a decisive role in its service performance. Therefore, it is of great significance to study the microstructure of ultrasonic assisted laser fusion composite coatings. In this paper, the grain growth of laser fused composite coating was studied by cellular automata method, and the reinforced particles were analyzed. The effect of non-uniform temperature field and ultrasonic vibration on the grain growth of composite coatings was studied. Based on the grain growth theory of grain boundary energy and curvature driven mechanism, the cellular automata model of grain growth for single-phase and two-phase materials was established. The effect of reinforced SiC particles on the grain growth of 316L stainless steel composite coating and AZ91D substrate was analyzed, and the evolution mechanism of ultrasonic assisted laser melt composite coating microstructure was studied. The following conclusions are obtained: The grain growth index is 0.34, and the grain size decreases with the increase of SiC content and the decrease of grain size. With the change of the depth of the molten pool, the temperature of the molten pool changes as an exponential function, and the grain size increases gradually. Under the inhomogeneous temperature field, the effect of pinning on the grain boundary increases with the increase of the content of SiC particles. The pinning effect increases with the decrease of SiC particle size. However, when SiC particle size is less than 10 渭 m, the grain refinement mechanism changes from grain boundary pinning to heterogeneous nucleation. (2) with the addition of SiC particles, the grain growth rate of magnesium alloy substrate becomes slower, and the grain size becomes smaller and more uniform; With the decrease of the size of SiC, the effect of pinning on the substrate structure is enhanced. The smaller the grain size of the substrate is, the more homogeneous the microstructure of Mg17Al12 phase is, and the easier it is to dissolve in 伪 -Mg matrix. 3) with the increase of ultrasonic amplitude, the nucleation rate of the melt increases, the grain size becomes smaller and the microstructure becomes more uniform. When the amplitude is 10 渭 m, the undercooling degree of the melt under ultrasonic vibration is 32.23 K. The nucleation rate is 279 times of that without ultrasonic vibration, and the grain refinement is obvious. In the SiC-316L experiment of ultrasonic assisted laser melting, the larger the content of SiC particles in the coating is, the smaller the grain size of the coating is. The more homogeneous the tissue is; The smaller the particle size of SiC is, the better the pinning effect of the coating is, and the smaller the columnar dendrite and the finer the grain of 316L coating after ultrasonic application, the simulation results are in good agreement with the experimental results.
【学位授予单位】：华东交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN249

【参考文献】